I got tired of monitoring FT8 signals on the 28 MHz band so I switched over to WSPR for a change. While I was listening during the morning, I heard an unusual signal on SSB.
It sounds like a slightly rough tone that lasts for about 7 seconds, stops for 1 second and then restarts as a different tone for another 10 seconds.
It then turns off for a second and the cycle starts again. The whole process seems to last for about 2-3 minutes.
The waterfall display above from the WSJT-X programme shows that the tones are in fact composed of several distinct frequencies.
It is not an amateur radio signal and I am assuming that it might be some sort of military OTHR (Over The Horizon Radar) signal but I have no idea about it's source?
Others must have heard this signal, anyone have any idea about its source???
Update: It looks as if this is Over The Horizon Radar (OTHR) from Iran.
"Ghadir, is an Iranian over the horizon radar Ghadir is a 360°, 3D-radar, with a ceiling of 300 km, and a maximum range of 1,100 km. You can hear a high and a low tone, corresponding to the sweep rates of 870 and 307 sweeps/sec. sent in two separated bursts."
This video from YouTube from IZ0KBA shows what it sounds like...
From the URE, the national body for radio amateurs in Spain..."New Radar OTH (Over The Horizon) in the 10-meter #radioamateur band. Received since the last week of October 2021. QRG: 28,000 kHz CF. AMOP. BW ca 45 kHz. 307 and 870 sps, alternately. IRN
This radar comes in addition to the Iranian one that broadcasts daily on 28,860 kHz CF, with the same bandwidth, but with a scan rate of 150 and 313 sps, alternatively.
The RADAR Over The Horizon Radar (OTH Radar, Radar beyond the horizon), is a type of radar system with the ability to detect targets at very long distances, typically hundreds to thousands of kilometers, beyond the radar horizon, which is the range limit for ordinary radar. Various OTH radar systems were deployed beginning in the 1950s and 1960s as part of early warning radar systems, but these have generally been replaced by airborne early warning systems.
The use of OTH Radars has receded nowadays, as the need for accurate long-term monitoring becomes less important with the end of the Cold War, and less expensive ground-based radars are once again being considered for functions such as maritime reconnaissance and surveillance of drug trafficking. However, old facilities are still in use and we are witnessing the creation of new ones.
Signal captured by the URE listening service, IARUMS URE (IARU Monitoring System, URE)."
Over The Horizon Radars (OTHR) are used by the military of several countries to detect planes and ships in distant locations.
While tuning across the 10 metre beacon band today, I came across an OTHR signal with a buzzing noise on 28.222 MHz. I used the FT8 waterfall display on WSJT-X to see what the signal looked like...
The Green horizontal lines are just the 15 second time stamps from the programme. What's of interest here are vertical lines which are spaced about 50 Hz apart. As you can see, it switches off at 08:44 UTC.
This is a video I found on YouTube which has a recording of the same type of signal but at a lower frequency....
